Various article fabricating machines and other machines utilize a desired predetermined sequential flow of equally spaced-apart workpieces therethrough during the fabricating or other operations by the machine. Devices have been proposed for such machines for monitoring this desired sequential flow of workpieces and operating control mechanisms for such machines in the event of the absence of a workpiece in the desired position of such sequential flow such as shown in application Ser. No. 549,049, filed Feb. 11, 1975, now U.S. Pat. No. 3,981,763, issued Sept. 21, 1976, and assigned to the assignee of the present invention. Such devices have for the most part included photoelectric cell mechanisms for sensing the passage of workpieces in the desired sequential flow.
The above types of machines include, inter alia, machines for fabricating individual articles in which it is desired to monitor the articles, machines for applying tabs, labels or strips to a continuous web of material during fabrication of articles from such web in which it is desired to monitor the tabs, labels or strips, and more specifically disposable diaper fabricating machines in which fastener tabs are applied at predetermined equally spaced-apart locations on each longitudinal edge of a continuous web of material being manufactured into such diapers in which it is desired to monitor the tabs applied to each longitudinal edge, such as shown in copending application Ser. No. 491,739, filed July 25, 1974, now U.S. Pat. No. 3,984,272, issued Oct. 5, 1976, and assigned to the assignee of the present invention.
The devices heretofore utilized with such machines for monitoring the predetermined spaced-apart sequential flow of workpieces or tabs, labels or strips were constructed for sensing the presence of such workpiece, tab, strip or label at the desired locations in the sequential flow for operating control mechanisms, such as stop devices or signalling devices in the event the sensing devices failed to sense such workpiece or tab, label or strip at each such location; however, were not constructed to sense the absence of workpieces, tabs, strips or labels between the desired locations in the sequential flow. Consequently, the sensing devices often malfunctioned and operated as though a workpiece, tab, strip or label was continuously present. Therefore, if such workpiece, tab, strip or label was absent of the desired locations or was improperly positioned between desired locations, the sensing mechanisms would fail to recognize this and the machine operation would continue with the improper positioning present.
This was particularly prevalent with photoelectric cell sensing devices in which the sensitivity thereof could be either improperly adjusted or be malfunctioning so that the photoelectric cell sensing means though it was sensing a workpiece, tab, strip or label continuously during the flow through such machines and failed to properly monitor and actuate the control mechanisms of the machine. Also, the reverse often occurred where the sensing device could malfunction to continually sense the absence of a workpiece, tab, strip or label.